This invention deals with a self-regenerating particulate filter useful in removing carbonaceous particulates and related hydrocarbonaceous materials from engine exhaust, particularly diesel engine exhaust. I have found by a proper selection of catalytic materials and by the method of introducing the catalytic materials into the particulate trap, that the particulate trap is able to self regenerate for long periods of time. By "self-regeneration," I mean that upwards of 95% of the carbonaceous and heavy hydrocarbonaceous particulate material introduced into a properly sized particulate trap is oxidized at the exhaust gas temperature. This being the case, the particulate trap need not be removed and treated in a furnace to remove carbon from the trap.
Diesel engine exhaust are known to contain, in addition to visible carbonaceous particulates, carcinogenic substances such as benzopyrene and nitropyrene. Removal of these carcinogens and particulate material is an ongoing problem. Although diesel engine exhausts are considered to be clean, apart from the carbon and unburned hydrocarbon components, removal of such materials is not trivial.
As noted above, particulate filters for diesel engine exhausts are known. These particulate filters encompass a wide variety of forms. They may be particulate or reticulated ceramic foam. They may encompass honeycomb-like structures, often with blocked passageways and small openings between adjacent passageways. Metal mesh filters, pelletized refractory materials such as alumina, and ceramic fibrous mats are all used as diesel particulate filters.
Common to all of these structures is the fact that after a reasonably short period of time, they become clogged with the material they are intended to remove. Virtually each structure noted above must be removed and heated, perhaps in a furnace or the like, to burn off the accumulated carbon and hydrocarbon oils so to, in effect, regenerate the particulate collector for reuse. These regeneration steps are carried out variously on the vehicle or in a furnace or the like.
Typical of the on-vehicle regeneration device is one found in U.S. Pat. No. 5,203,166, to Miller. Miller describes an emissions control system to be installed on a diesel engine exhaust. It includes a particulate filter system and a pair of heaters. The heaters operate in such a way that one portion of the catalyzed particulate filter system is being regenerated while the rest is being used. Miller does not appear to describe the kind of catalyst which is used.
European Patent Application No. 0,321,451 also describes a diesel particulate oxidizer placed in an exhaust system. Of major interest in the '451 patent, however, is the control system used to regenerate the device. Although the support is said to be a ceramic foam, little else is said about the makeup of the catalyst.
Similarly, EPO 590,814 is, in the main, heavily involved with the procedures for regenerating and the device is used in monitoring and reviving the soot collection catalyst. The oxidation catalyst is said to be platinum, palladium, or a platinum-palladium alloy. No other catalyst type is mentioned.
European Patent Application No. 0,703,352 similarly is concerned with an emission control system rather than the oxidation catalyst itself. No specific catalyst is noted in the description of the invention.
European Patent Application No. 0,743,429 describes a diesel exhaust particulate filter which includes an oxidation catalyst. The oxidation step is controlled by the introduction of diesel fuel upstream of the oxidation catalyst and the fuel is burned to raise the temperature of the exhaust cast and hence the catalyst bed to burn away the particulate material found in the filter. Again, no specific type of catalyst is described.
Finally, European Patent Application No. 0,764,455 shows the use of a sintered fiber web as the device for removing carbon-based particles from the exhaust gas. The web may be treated to form an alumina film on the surface of the fibers and optionally a catalyst may be placed on those alumina-coated fibers. The catalytically active materials are described quite broadly as "at least one kind of metal selected from the group consisting of the metals of Group 1, Group 2, Group 3b, Group 4b, Group 5b, Group 6b, Group 7b, or Group 8 of the Periodical Table."
More important to this invention are the patents dealing with a specific oxidation catalyst useful for placement in diesel engine exhaust filters for oxidizing particulate materials found there.
U.S. Pat. No. 4,510,265, to Hartwig, describes a diesel engine exhaust gas catalyzed filter which is said to be self-cleaning. The active oxidation catalyst is said to be a combination platinum and silver vanadate material. The example shows removal of accumulated carbon by placement of the filter in a furnace variously at temperatures of just greater than 475.degree. C. (for 20% burnoff) to just over 600.degree. C. (for 80% burnoff).
U.S. Pat. No. 4,711,870, to Yamada et al., similarly shows a porous ceramic body used to oxidize diesel soot. The active catalyst is said to be one comprising: (a) copper or a copper compound; (b) vanadium or a vanadium compound; (c) zirconium, aluminum, nickel, iron, manganese, lanthanum, chromium, zinc, lead or cerium, or a compound thereof; and optionally, (d) platinum, rhodium, or palladium, or a compound thereof. These catalysts are also said to allow the particulate burning temperature to be lowered below that required prior to the date of the Yamada et al patent. The temperature for removing 90% of the soot found in a control sample of the catalyzed porous body is shown in example 12 to be in the neighborhood of 460 to 470.degree. C. The conversion of sulfuir dioxide to sulfur trioxide was shown to be typically between 15 and 33%.
U.S. Pat. No. 4,759,918, to Homeier et al., shows a Platinum Group metal (platinum, palladium, or rhodium) as a catalytic soot removal device. Example 6 of the patent shows a diesel soot combustion efficiency of 95% at 400.degree. C. by use of a platinum catalyst on a titania support.
U.S. Pat. No. 5,000,929, to Horiuchi et al., shows a similar catalyst for diesel soot removal made up of a support, typically of an inorganic refractory oxide, and having palladium and the oxide of at least one of praseodymium, neodymium, and samarium as components.
U.S. Pat. No. 5,213,781, to Abe et al., and its division, U.S. Pat. No. 5,340,548, describe a porous diesel engine exhaust filter also catalyzed. The active catalyst is said to be made up of an alkali metal, a copper metal, a vanadium element, and at least one rare earth element. The particulate matter is said to be oxidized at 400.degree. C. using Abe et al's catalyzed ceramic filter.
U.S. Pat. No. 5,294,411, to Breuer et al., describes an electrically heated catalyst carrier body utilizing rhodium or platinum as the oxidizing catalyst.
U.S. Pat. No. 5,330,945, to Beckmeyer et al., shows a diesel fuel exhaust filter containing a zeolite-based wash coat material. The preferred Y-type zeolite is exchanged with a precious metal to form the active material.
European Patent Application No. 0,714,652, to ICT Company Ltd., shows a catalyst for treatment of diesel engine exhaust gas comprising a three-dimensional support structure coated with a platinum and/or a palladium carrying refractory inorganic oxide powder further containing a metal selected from the group consisting of tungsten, antimony, molybdenum, nickel, vanadium, manganese, iron, bismuth, cobalt, zinc, and the alkaline earth metals.
European Patent Application No. 0,508,513, to General Motors Corporation, shows use of a Y-type zeolite supported on a ceramic or a metal monolith. The monolith is used in treating diesel fueled engine exhaust.
EPO No. 0,160,482, to Engelhard Corporation, shows a self-cleaning diesel exhaust particulate filter having as its oxidic catalyst mixture, a platinum group metal and an alkaline earth metal. Oxidation temperatures in the neighborhood of 350.degree. C. appear to have been achieved using such technology.
EPO No. 0,600,442, to Nippon Shokuvai Company, utilizes iron as the active catalytic component in a diesel engine exhaust gas purification catalyst.
EPO No. 0,658,369 utilizes a diesel exhaust trap utilizing an oxidizing catalyst made up of platinum, rhodium, copper or vanadium oxide, composite oxides such as perovskites such as LaMnO.sub.3 and LaCrO.sub.3, a part of which may be replaced with alkali metals or alkaline earth metals such as strontium, potassium, or lithium. The examples showed initial oxidation temperatures (for carbon particulates) to be from about 280.degree. to 427.degree. C.
EPO No. 0,092,023, owned by the Bridgestone Tire Company shows a diesel exhaust trap having an oxidation catalyst of metallic copper or copper compound, metallic molybdenum, metallic vanadium, a molybdenum or vanadium compound, and an alkali metal compound. The catalytic material is preferably placed on a carrier of titania, .gamma.-alumina, or silica-alumina. It is preferably used with a metallic platinum, palladium, or rhodium component for enhanced catalytic activity.
None of these patents and documents show the invention as described and claimed below.